It's no secret that we humans tend to put a bit more padding on our bones compared to our closest living primate relatives. Even without a diet with donuts and Netflix, evolution has left bodies that hoard fat.
An analysis of adipose tissue from various primates has revealed that some of these are due to subtle differences in the way in which cells package DNA. This makes it difficult for us to convert our spare tire into easily combustible fat.  Biologists at Duke University found that unlike chimpanzees and macaques, we humans do not have easy access to sets of calorie-converting genes in our fat cells. As a result, the rich supply of lipids found in our adipose tissue is usually preserved unless we work overtime to burn it.
This is not a recent phenomenon caused by the lifestyle of couch potatoes. While other primates in the wild have less than 9 percent body fat, healthy people can easily carry twice this amount.
"We are the fat primates," says Devi Swain-Lenz, a functional Genomics researcher at Duke University.
Such a significant metabolic difference becomes all the stranger the less the random sequence of human and chimpanzee DNA differs by a few percent.
To Learn How Small Differences in Coding Can Account for Big Differences Unlike the waist, Swain-Lenz and her team sampled fat-storing adipose tissue from chimpanzees, humans, and a more distant relative, the rhesus monkey.
There are two types of fatty tissue that you need to know: brown and white. Brown adipose tissue keeps its fat in tiny droplets surrounded by energy-transforming mitochondria. Its main purpose is to rapidly promote heat generation in the event of temperature drop by driving trembling muscles.
Meanwhile, white grease stubbornly sticks to its reserves and not only provides a substitute fuel supply, but acts as a physical protective layer and thermal insulation. It is this tissue that expands in times of high volumes and the type of fat that researchers were most interested in.
To better understand what could happen at the genetic level, the team searched for DNA areas that were open to the business & # 39 ;. Long DNA strands are typically wrapped in protective cells and wrapped around proteins. Their exposed segments are the easily accessible templates that amplify and enhance sequences.
These so-called open chromatin regions differed significantly between humans and the other two primates. In fact, just under 3,000 human regions were either easier or less accessible than chimpanzees.
Importantly, many of the 780 less accessible segments in humans regulated adjacent genes, much of which were related to fat metabolism.
One of these buried sequences, a transcription factor called Nuclear Factor 1
The gene of the protein is quite similar in humans and in chimpanzees, but it is less The revelation in our pooled DNA could help to explain important differences as to why we tend to build more white fat than brown.
It raises some interesting questions as to why humans have evolved over the past millions of years to bury these fat-converting regions. We separate ourselves from chimpanzees.
The size of the brain seems to be a convenient answer. As our size tripled, the chimpanzee brains barely moved. The energy requirement of a larger nervous system is considerable. Therefore, it makes sense that our body in the form of abundant white fat provides additional security in our energy reserves.
However, just because we've ransacked our genes, that does not mean we can just correct our fat distribution.
"Perhaps we could find a group of genes to switch on or off, but we are still a long way off," he tells Swain-Lenz.
"I do not think it's that easy to push a switch, if that were the case, we would have found out long ago."
This study was published in Genome Biology and Evolution .